Hello, so the child seems to have undergone all possible investigations n the problem seems to be due to his anxiety issues. How about his sleep pattern n eating habits?
Next Steps
Does he have any major issues at school or among his peers? He needs to have some regular counselling sessions with a therapist n then things shall settle otherwise these issues might continue God forbid.
Health Tips
Meanwhile we need to pay special attention to his diet n sleep. Do avoid spicy, fried n junk food. Give him lots of water. Try to spend more time with him, certain family outings will help too. He needs more of love, affection and empathy during this phase.